1. Field of the Invention
This invention relates to an electrophotographic roller member (hereinafter also simply “roller member”) used in, e.g., developing rollers which carry toners thereon, used in electrophotographic image forming apparatus.
2. Description of the Related Art
Conventionally, electrophotographic image forming apparatus such as copying machines and laser printers have developing rollers.
In the electrophotographic image forming apparatus, a contact developing system with a non-magnetic one-component toner and a non-contact developing system with a magnetic one-component toner are in wide use. The contact developing system is a system in which a non-magnetic toner is coated on a developing roller by means of an elastic blade or the like and a voltage is applied in the state the developing roller and a photosensitive drum are in contact with each other, to make the toner move to electrostatic latent images formed on the photosensitive drum to perform development. The non-contact developing system is a system in which a magnetic toner is bound onto a developing roller by magnetic force of a built-in magnet and the level of the toner is controlled by a control means, where a voltage is applied in the state the developing roller and a photosensitive drum are not in contact with each other, to make the toner fly to electrostatic latent images formed on the photosensitive drum to perform development.
For example, in the contact developing system, the non-magnetic toner is transported to a developing zone in the state it is carried on the surface of the developing roller, which is rotated in contact with the photosensitive drum. Then, in that contact zone, the non-magnetic toner moves from the developing roller to the photosensitive drum in accordance with a pattern of the electrostatic latent images. Where the developing roller is a cylindrical drum of popular use, a conductive rubber roller having a mandrel and formed on its peripheral surface a conductive elastic layer is usually used as the developing roller, in order to secure a stable contact width between it and the photosensitive drum.
In such a conductive rubber roller, it is well known that, in order to prevent the elastic layer from wearing and prevent the toner from adhering to the surface of the developing roller to cause filming, a single-layer or multiple-layer film is further formed on the elastic layer. As one of methods for forming such a film, Japanese Patent Laid-open Application No. 2007-010764 discloses a developing roller having a good dimensional precision, a cover layer of which is formed by dip coating.
However, where a film is formed by coating, it is usually necessary to provide the step of drying and hardening a wet coating. Where it is necessary to heat it in such a drying step, materials for the elastic layer are required to have heat resistance. Hence, the materials for the elastic layer may inevitably be limited. Also, where a solvent is used, it may take much time and labor to deal with the solvent after use.
Meanwhile, Japanese Patent Laid-open Application No. H01-257970 discloses a toner carrying member having on its surface a film comprising a semi-conductive layer formed of a ceramic having a specific resistance of from 104Ω·cm or more to 1012Ω·cm or less, which is formed by plasma spray coating and is further subjected to sealing treatment. Japanese Patent Laid-open Application No. H01-144078 also discloses a toner carrying member having a ceramic coating layer of from 0.1 μm to 5.0 μm in a thickness, formed by coating carried out in the presence of plasma formed; the layer being formed by plasma CVD or the like. However, both the above Japanese Patent Laid-open Applications No. H01-257970 and No. H01-144078 disclose formation of the film on a substrate made of stainless steel or aluminum, and neither disclose nor suggest any formation of the film on the surface of an elastic layer.
As the electrophotographic image forming apparatus have been made high-minuteness and high-speed in recent years, the electrophotographic roller member has also come to be required to have performance in a higher grade. In particular, the roller member is required to be much more improved in dimensional precision such as roundness (cylindricality). Accordingly, as a method of forming a film, the present inventors have repeatedly made studies on formation of a film on an elastic layer by the plasma CVD disclosed in the above Japanese Patent Laid-open Application No. H01-144078. As the result, they have come to a finding of film forming conditions which are favorable for forming a cover layer on the elastic layer by plasma CVD to obtain an electrophotographic roller member having a high dimensional precision.